The following background information is provided to assist the reader to understand the invention described and claimed below. Accordingly, any terms used herein are not intended to be limited to any particular narrow interpretation unless specifically stated otherwise in this document.
For a train headed by a locomotive equipped with the conventional brake control system, a pneumatic trainline known as the "brake pipe" is the only means by which service and emergency brake commands are conveyed to each of the railcars in the train. The brake pipe is essentially one long continuous tube that runs from the lead locomotive to the last railcar in the train. The brake pipe is actually composed of a series of interconnected pipe lengths, with one pipe length secured to the underside of each railcar. The brake pipe is formed by connecting each pipe length via a coupler to another such pipe length on an adjacent railcar. As shown in FIG. 1, it is to this brake pipe 1 that the pneumatic brake equipment on each railcar connects via a branch pipe 2.
The pneumatic brake equipment on each railcar includes two storage reservoirs 3 & 4, one or more brake cylinders 5 and at least one pneumatic brake control valve 6 such as an ADB, ABDX or ABDW type valve made by the Westinghouse Air Brake Company (WABCO). Under conditions known in the brake control art, the pneumatic brake control valve 6 charges the two reservoirs 3 and 4 with the pressurized air it receives from the brake pipe 1. It is the pressure level within the brake pipe 1 that determines whether the brake control valve 6 will indeed charge these reservoirs or deliver pressurized air previously stored in one or both of these reservoirs to the brake cylinders 5. When so pressurized, the brake cylinders 5 convert the pressurized air that they receive from the brake control valve 6 to mechanical force. From the brake cylinders this force is transmitted by mechanical linkage to the brake shoes. The magnitude of the braking force applied to the wheels is directly proportional to the pressure built up in the brake cylinders. Forced against the truck wheels and/or disc brakes, the brake shoes are used to slow or stop the rotation of the wheels. For trains equipped with the conventional brake control system, it is thus the pressure level in the brake pipe 1 that determines whether and to what extent the railcar brakes will be applied.
In addition to the brake pipe, the locomotive has its own pneumatic trainlines including a main reservoir equalizing (MRE) pipe, an independent application and release (IAR) pipe, and an actuating pipe. Within a locomotive consist (i.e., two or more locomotives connected together), the MRE, actuating and IAR pipes of each locomotive connect to the MRE, actuating and IAR pipes of adjacent locomotives. The MRE pipe is used to charge the brake pipe to a normal operating pressure of approximately 90 psi when the brakes are released. Incidentally, it is the pressure within the IAR pipe that controls the delivery of pressurized air to, and thus the operation of, the brakes of the locomotive(s) in the train.
The locomotive also features a multi-wire electrical trainline known as the multiple unit (MU) line cable. The MU line cable consists of twenty seven (27) different electrical lines. As is well known in the railroad industry, the MU line cable contains an alarm line on which the locomotive equipment can convey various signals to alert the train operator of critical conditions occurring in the locomotive. The MU line cable also contains 74V dc power and return lines on which battery power from the locomotive is supplied to the various power consuming devices on the train.
There are many different types of conventional brake control systems in use in the railroad industry. An example of one type of conventional brake control system is the 26-L Locomotive Air Brake Control System manufactured by WABCO. A conventional brake control system, such as the 26-L System, has two brake handles referred to as the automatic and independent brake handles. By placing these handles into the appropriate positions, a train operator in the locomotive can control how the brakes on the locomotive(s) and railcars operate. More specifically, by moving these handles into the proper position, the train operator can control how much pressure will be developed in the IAR and brake pipes, as well as in the other pneumatic trainlines of the train. It is by such control of the pressure level in the brake pipe 1, for example, that the pneumatic brake equipment on each railcar is controlled.
By moving the independent brake handle, the train operator can direct the conventional system only to apply or release the brakes on the locomotive(s). In contrast, by moving the automatic brake handle, the operator can direct the brake control system to apply or release the brakes on both the locomotive(s) and railcars in the train. The level to which the system reduces or increases pressure within the brake pipe 1, and thus the amount of braking power exerted by the train brakes, ultimately corresponds to the position of the automatic brake handle. The automatic brake handle can be moved from and in between a release position at one extreme (in which brake pipe pressure is maximum and the brakes are completely released) to an emergency position at another extreme (in which brake pipe pressure is zero and the brakes are fully applied).
The positions for the automatic brake handle include release, minimum service, full service, suppression, continuous service, and emergency. Between the minimum and full service positions lies the service zone wherein each incremental movement of the automatic brake handle toward the full service position causes an incremental reduction in brake pipe pressure. The exact amount by which the brake pipe pressure is reduced depends on how far towards the full service position the brake handle is moved. It is this reduction in pressure that signals the pneumatic brake control valve(s) 6 on each railcar to supply pressurized air from one or both reservoirs to the brake cylinders so as to apply the railcar brakes. The amount of pressure built up in the brake cylinders, and thus the magnitude of the braking force applied to the wheels, is proportional to the amount by which the brake pipe pressure has been reduced.
When the automatic brake handle is moved from within the service zone or above towards the release position, the way in which the brakes operate depend on whether the brake equipment has been designed to allow a graduated release of the brakes. Passenger trains typically feature brake equipment that allows a graduated release of the brakes when the locomotive brake control system is set in the "passenger service" mode of operation. Freight train brake equipment, in contrast, typically permits only a direct release of the brakes.
For direct release equipment, in response to such movement of the automatic brake handle, the brake control system does not command an increase in the pressure within the brake pipe 1 until the automatic brake handle is placed in the release position. Once the pressure in the brake pipe increases above a preset level (e.g., 2 psi), the control system and the railcar brake control valves it affects respond by completely venting the brake cylinders thereby fully releasing the train brakes.
For graduated release equipment, in response to such movement of the automatic brake handle toward the release position, the brake control system commands an increase in the pressure in the brake pipe incrementally. The level to which the brake pipe pressure rises is dependent on the extent to which the automatic brake handle is moved toward the release position. Unlike the locomotive brake control system and pneumatic brake control valves for direct release equipment, those designed for graduated brake release react to this incremental rise in brake pipe pressure by reducing proportionately the pressure in the brake cylinders thereby reducing the force with which the train brakes are applied.
For a train headed by a locomotive equipped with the newer ECP based brake control system, brake commands are primarily conveyed to each of the railcars electrically via a two wire ECP trainline. Specifically, both service and emergency brake commands are communicated electrically via this ECP trainline to the ECP brake equipment on each railcar in the train. The ECP brake equipment on each railcar is basically the same as the pneumatic brake equipment previously described, except for the pneumatic brake control valve 6. As is well known in the art, a car control unit (CCU), one or more pressure transducers and various pneumatic and electropneumatic valves are used in lieu of the pneumatic brake control valve. The pressure transducers are used to monitor pressure within the brake pipe and the brake cylinders as well as the pressure within the two reservoirs. Akin to the branch pipe 2 shown in FIG. 1, branch wiring is used to connect the CCU to the ECP trainline. Supplied from the 74V dc power line of the MU line cable in the locomotive, the ECP trainline operates at a nominal 230V dc to power the ECP brake equipment on each railcar.
For railcars equipped with ECP brake equipment, the brake pipe 1 still serves as the source of pressurized air from which to charge the reservoirs 3 & 4 on each railcar. During service and emergency braking, it is still from one and both reservoirs, respectively, that pressurized air is delivered to the brake cylinders 5 to apply the railcar brakes. In the ECP brake control system, however, the brake pipe is not used to convey service brake commands. It is used only to convey emergency brake commands as a pneumatic backup to the electrical emergency brake commands conveyed along the ECP trainline. Should the ECP brake equipment lose power or otherwise fail electrically, it generally will respond pneumatically to an emergency pressure reduction in the brake pipe by supplying pressurized air from both reservoirs to the brake cylinders thereby causing an emergency application of the railcar brakes.
The ECP based brake control system in the locomotive includes a cab station unit and a master controller from which the brakes on the train are ultimately controlled. Inputs from handle(s) or push buttons are processed by the cab unit and then passed to the master controller. Operating according to instructions contained within its programming code, in response to these and other inputs, the master controller formulates a brake command appropriate to current conditions and transmits it along the ECP trainline to each of the vehicles in the train. The brake command and other ECP messages are transmitted over the ECP trainline via a powerline communications system such as the Echelon LonWorks System specified by the American Association of Railroads (AAR). The master controller can order through the brake command any action from a release of brakes to an emergency application of brakes or any degree of brake application in between those two extremes. The brake equipment may also be designed to provide graduated release of the brakes. The degree of brake application ordered by the master controller is typically conveyed in terms of a percentage of the pressure required for full service brake application. Zero percent (0%) is typically designated for a release of brakes, 15% for a minimum service brake application, 100% for a full service brake application and 120% for an emergency brake application.
Each CCU includes a transceiver device and a microprocessor unit. Controlled by the microprocessor unit, the transceiver is connected via the branch wiring to the ECP trainline from which it receives the electrical brake commands issued by the master controller. The transceiver converts the electrical brake command into a form usable by the microprocessor. In a manner well known in the brake control art, the microprocessor controls the aforementioned electropneumatic valves through which pressurized air can be supplied to or exhausted from the brake cylinders 5 on the railcar according to the dictates of the particular electrical brake command received.
The communications network on board an ECP based train is typically comprised of the master controller and powerline communication system in the lead locomotive and the CCU on board each railcar as well as the ECP trainline over which they communicate. The master controller is responsible for most of the communication over the ECP trainline in that it broadcasts the most recently formulated brake command to all railcars in the train. The master controller also polls the railcars at a predetermined rate (e.g., every second). Each CCU has its own unique identification code that it transmits to the locomotive when polled by, and reporting information about its operations to, the master controller. Specifically, sequentially or according to other criteria, the master controller sends a status query addressed to one railcar to determine whether the selected CCU is attentive to the brake control system. When so queried, a selected CCU will normally respond to the interrogation unless it has lost the ability to communicate which in itself provides an indication of its status to the master controller. Taking the form of the identification code, the response to the query also typically includes other ECP operational data such as brake pipe pressure, brake cylinder pressure, battery voltage, reservoir pressure(s) and whether the brakes on the railcar or one of its trucks are cut-in (enabled) or cut out (disabled). By its response, the selected CCU informs the master controller that it is a properly operating part of the ECP brake control system. Separate from the polling cycle, a CCU can send on its own initiative an alarm message. Each railcar via its CCU can thus report to the master controller critical data and other diagnostic information should any of the following conditions occur: improper brake cylinder pressure, failure of a reservoir to charge, abnormally low pressure in the brake pipe or in one of the reservoirs or failure to receive communications. The CCU may also issue specific control messages in response to various other circumstances as is well known in the brake control art.
Many trains, whether equipped with ECP or conventional brake control systems, are also rigged with any one of several known end-of-train (EOT) radio telemetry systems. These systems typically include a locomotive control unit (LCU) located in the locomotive and an EOT rear unit mounted to the last railcar in the train. The EOT unit is coupled to the brake pipe on the last railcar by means of a hose and a glad hand. In a one-way EOT system, the EOT unit transmits by radio signals to the LCU data pertaining to the pressure in the brake pipe and the motion of the last railcar. To accomplish this, the EOT unit includes a pressure transducer to monitor brake pipe pressure, a motion sensor to sense movement of the railcar, a microprocessor unit to control the overall operation of these components and a transmitter that the microprocessor unit uses to transmit this last railcar data. In the locomotive, the LCU includes a primary display, a receiver to receive transmissions from the EOT unit and a microprocessor unit. Controlled by the microprocessor unit, the display is used to convey the last railcar data to the train operator. Furthermore, in response to an emergency command transmitted by the EOT unit, the LCU will also display that an emergency condition exists at the rear of the train. The EOT unit is typically configured so that the emergency condition represents a sudden loss of brake pipe pressure or a drop in brake pipe pressure below a predetermined level.
For a train equipped with a one-way EOT system, the emergency brake application starts at the locomotive and progresses along the brake pipe to the last railcar. For long trains, reducing the pressure in the brake pipe from the head of the train can be quite time consuming, particularly for a train equipped with a conventional pneumatic brake control system. Moreover, if one of the angle cocks is left closed or the brake pipe is otherwise restricted, the brake equipment beyond the restriction may not receive the emergency brake command needed to apply the brakes in an emergency. For this reason, two-way EOT systems have been developed under the auspices of the AAR.
In a two-way EOT system such as the TRAINLIN.RTM. II EOT system manufactured by WABCO, the LCU and EOT unit still perform all of the functions attributed to their counterparts in the one-way EOT system. The EOT unit is thus still used to transmit the aforementioned radio signals by which last railcar brake pipe pressure and motion data is conveyed to the LCU. The twoway EOT and LCU units, however, are each equipped with a transceiver (i.e., combination transmitter and receiver) as compared to the single transmitter and receiver for the one-way EOT and LCU units, respectively. The EOT unit also has an emergency brake valve that is controlled by its microprocessor unit, and the LCU also includes an emergency toggle switch. By toggling this switch in an emergency, the train operator can cause the LCU to transmit an emergency brake radio signal to the EOT unit. By its microprocessor unit, the EOT unit responds to this emergency signal by commanding its emergency brake valve to reduce the pressure in the brake pipe at an emergency rate. Combined with the emergency reduction in brake pipe pressure initiated from the head end of the train using the aforementioned brake systems, the two-way EOT system allows an even faster application of the railcar brakes in an emergency.
In this two-way EOT system, the LCU has a primary display panel which features a dedicated display for each of several types of last railcar data. The last railcar data displayed includes brake pipe pressure, low battery condition, whether the railcar is stopped or in motion, and whether an emergency has been enabled or disabled. The LCU also has a supplemental message display by which it visually conveys additional information such as, for example, data related to arming of the EOT system and whether or not the EOT unit and LCU are communicating properly.
For a train equipped with a conventional pneumatic brake control system wherein the brake pipe is used to pneumatically convey both service and emergency brake commands to the railcars, another EOT radio telemetry system, such as the TRAINLINK.RTM. ES system manufactured by WABCO, may be used. It is, of course, well known that an emergency application is initiated at a rate much faster than a service application. Typically, the emergency reduction in pressure propagates along the brake pipe at a speed of approximately 900 feet/sec. Consequently, for a one mile long train, the propagation time would be in the range of 10 to 15 seconds. In contrast, a service application can take well over a minute to reach the last railcar; hence the need for, and development of, the TRAINLINK.RTM. ES system.
In addition to the two-way LCU and EOT units, the TRAINLINK.RTM. ES system has a Service Interface Unit (SIU) that connects between the serial port of the ES LCU and the brake pipe on the locomotive. The SIU provides the ES LCU with the current brake pipe pressure. This allows the ES LCU to automatically initiate a service brake application at the last railcar simultaneously with the service reduction in brake pipe pressure initiated from the locomotive. Specifically, the ES LCU in the locomotive automatically transmits a service brake radio signal to the ES EOT unit when it detects a service reduction in brake pipe pressure via the SIU. By its microprocessor unit, the two-way ES EOT unit responds to this service brake signal by commanding its valve to reduce the brake pipe pressure from the last railcar at the same service rate as that ordered by the brake control system in the lead locomotive at the head of the train. A service application of the brakes can thus be made much faster on a train equipped with a TRAINLINK.RTM. ES or similar type EOT system. Using the SIU, the ES LCU can also automatically transmit an emergency brake signal when an emergency reduction in brake pipe pressure has been initiated by the brake control system in the locomotive. The emergency toggle switch on the ES LCU can also be used to transmit this emergency brake signal.
Lead by the American Association of Railroads (AAR), the railroad industry, particularly for freight trains, is encouraging the development of the newer ECP based brake control systems. This is because ECP brake control systems perform far better, and are far more capable, than their older pneumatic counterparts. An ECP based system, for example, can apply and release the railcar brakes much faster than any of the conventional pneumatic brake control systems. For a conventional system, the speed at which the brakes react is relatively slow as it takes time, especially for long freight trains, for the pneumatic brake commands to propagate the length of the brake pipe. For an ECP based system, the speed at which the brakes react is much faster as the brake commands are conveyed electrically to the railcars. Furthermore, unlike railcars equipped with conventional pneumatic brake equipment, railcars equipped with ECP brake equipment communicate with the locomotive. Not only does it act upon the electrical brake commands received from the master controller, the ECP brake equipment on each railcar also reports to the locomotive the aforementioned ECP data (i.e., data about its own operations).
As the railroad industry converts to ECP based brake control systems, it faces several logistical problems typical of such transitions. The first ECP equipped trains put in operation have typically been limited to operating as "unit trains" (i.e., a group of railcars each equipped with ECP brake equipment and operated as a single train). Most of the larger railroad operating authorities, however, are not able to dedicate a locomotive solely to a particular unit train. For a railroad authority to operate a unit train on a consistent basis, it would need to equip a large number of its locomotives with ECP brake control systems. Further complicating matters is that a given unit train must often travel over several territories each operated by a different railroad authority. Consequently, a given unit train may be hauled by several different locomotives en route to its destination.